1. Field of the Invention
This invention relates to a primer composition. More particularly, this invention relates to a primer composition which will strongly adhere a room temperature-curable silicone rubber or a room temperature-curable silicone-modified organic rubber to the surface of a substrate which is in contact with the rubber as it is curing.
2. Description of the Prior Art
Large amounts of room temperature-curable silicone rubber have recently been used as construction sealants because the durability of the rubber itself is far superior to the durability of other organic rubbers. Room temperature-curable silicone-modified organic rubbers have recently been developed and their application as construction sealants has been attempted. Various types of substrates are used in construction and include metals such as aluminum, steel, and stainless steel; coated building materials such as acrylic resin-coated, urethane resin-coated or epoxy resin-coated aluminums; hard inorganic building materials such as glass, tile and stone and porous inorganic substrates such as mortar, concrete, and autoclaved light weight concrete. For this reason, the strong adhesion of a room temperature-curable silicone rubber or a room temperature-curable silicone-modified organic rubber to the above-mentioned substrates is an important subject. In order to strongly adhere the substrate to the rubber, the substrate is usually treated with various primers and coated with a room temperature-curable silicone rubber or a room temperature-curable silicone-modified organic rubber followed by curing. However, among the above-mentioned substrates, pure aluminum, surface-treated aluminum, stainless steel, various resin-coated aluminums, and mortar are not good substrates for adhesion, with the result that a silicone rubber sealant or silicone-modified rubber sealant will peel at the interface with the substrate before it will degrade or lose its rubber elasticity. For this reason, the development of a primer which exhibits a long-term high adhesive strength, particularly a long-term high adhesive strength when immersed in water, is in demand.
A primer composition composed of an epoxy resin and an aminoalkylalkoxysilane is disclosed in Example 9 of Japanese Kokai No. 53-79929, published July 14, 1978 to Toshiba Silicone K.K., and naming as inventors I. Endo and C. Shimizu; however, this primer composition exhibits poor adhesiveness and gels in a short period of time due to the high reactivity of the amino groups of the aminoalkylalkoxysilane with the epoxy groups of the epoxy resin. Thus, it suffers from the drawback of no storage stability. Various methods were investigated by the present inventors in order to develop a primer composition which would provide strong and long-term adhesion between a room temperature-curable silicone rubber or a room temperature-curable silicone-modified organic rubber and various substrates, and which would itself exhibit excellent storage stability. The primer composition of this invention was developed as a result of this investigation.